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PROCEEDINGS OF THE ACADEMY OF 
unite” Cryptonella and Centronella “until a reexamination of the original 
specimens of Mr. Billings shall confirm his first observations, or show them to 
correspond with” Cryptonella. It is this hesitation to admit the inevitable 
consequence, and to retract his honorable and friendly, but unfounded criti¬ 
cism, which induces me to reassert the correctness of my generic reference of 
Centronella Julia , resting as it does upon the original description and figure, 
and the observed characters of the type of the genus, as well as the subsequent 
confirmation of the author of the genus, himself. 
OSTREA, Linnaeus. 
Ostrea patercula, n. sp. Shell adherent, thin, small, ovate, deeply boat¬ 
shaped, with the deeply excavated beak of the lower valve prominent, incur¬ 
ved and somewhat posterior. The muscular scar is large, transversely broad- 
reniform, concave on the cardinal side, situated nearly midway between the 
centre of the valve and its posterior margin, and is marked by two transverse 
lamellose lines. The deepest part of the valve is midway between the centre 
and the beak ; the depth is nearly the same for as great a distance on the 
other side of the centre. The exterior of the shell is irregular with concen¬ 
tric lamellose lines of growth. 
Greatest length, *65 (100) ; greatest width, *40 (61) ; greatest depth of 
lower valve, *25 (35) ; depth of cavity of the beak, *15 (23). 
From the buff sandstone at the base of the Burlington limestone, Burling¬ 
ton, Iowa. “ White Collection ” of the University of Michigan. 
The unexpected discovery of this oyster—believed to be the most ancient at 
present known—together with its somewhat cretaceous aspect, awakened a 
suspicion that it had not been found in place. To certify myself on this point, 
I addressed Dr. White on the subject, and received the following reply : “The 
Ostrea , if I remember rightly, was imbedded in a white or light gray, silicious 
material, of chalky appearance, containing some remains of crinoids and shells. 
My impression is, also, that it was from a quarry about half a mile north of 
my residence, and in the lower bed of the Burlington limestone, and not far 
from its base. I think the label which accompanied it, and also my letter at 
the time, may be entirely relied on. I admit the possibility of error, but I do 
not believe there is any.” 
Pterinea crenistriata, Win. ( Cardiopsis crenistriata, Win., Proc. Acad. 
Nat. Sci. Phil. Sept. 1862, p. 417.) More perfect specimens from the typical 
w locality of C. crenistriata reveal the fact that the species is possessed of an an¬ 
terior wing, which is a mere flattened portion of the anterior angle of the car¬ 
dinal line, with a barely perceptible sinus beneath. This feature does not 
belong to Cardiopsis as defined, and establishes a probable conformity with 
Pterinea. 
The right valves—recently discovered—might be mistaken for another spe¬ 
cies. They show no radiating lines, except near the hinge, behind the beak. 
The concentric markings are only small, irregular wrinkles of growth, with 
none of the sharply raised lines which characterize the other valve. It is of 
course possible that these right valves belong to another species, but as they 
have exactly the form of the crenistriated valves, and the latter are all left 
valves, it seems probable that they belong together. 
Pterinea spinalata, n. sp. ( Avicula acanthoptera, Win., Proc. Acad. Nat. 
Sci. Jan. 1863, p. 8 ; not A. acanthoptera , Hall, Geol. Rep. 10th Dist. N. Y. p. 
263.) Careful comparison with the types of A. acanthoptera , Hall, convinces 
me that the Iowa specimens ought to be separated. The left valve of A. acan- 
thoptera , Hall, has the body of the shell broader than in the Iowa specimens, 
and both wings are less defined. The right valves, also, are much flatter. 
Amongst the Iowa specimens appear to be two types—one with the body of 
the valve arcuate, and the other with it straight. The former type was 
[July, 
